This invention relates to a method of preparation of ethylene-alpha,beta-ethylenically unsaturated carboxylic acid copolymer salts; more particularly, this invention relates to the preparation of the metallic salts of low molecular weight copolymers of ethylene and an alpha,beta-ethylenically unsaturated carboxylic acid.
It is known in the art to produce ionic metal salts from copolymers of at least one alpha-olefin of a general formula RCH.dbd.CH.sub.2 where R is a radical selected from the class consisting of hydrogen and alkyl radicals having from 1 to 8 carbon atoms, and an alpha,beta-ethylenically unsaturated carboxylic acid. Such ionic hydrocarbon polymers and processes for preparing them, as well as processes for preparing ionically crosslinked copolymers are described in U.S. Pat. Nos. 3,264,272; 3,649,578; 3,969,434; 3,404,134; 3,789,035; 3,970,626; and 3,779,952.
A review of the art, including the above-noted patents, shows that the prior art copolymer salts and processes for making them are generally directed to salts made from relatively high molecular weight copolymers. The reaction is generally carried out at superatmospheric pressures as high as 10,000 psi.
Attempts to form metallic low molecular weight copolymer salts of ethylene and alpha,beta-ethylenically unsaturated carboxylic acids at atmospheric pressure or higher pressures have resulted in reaction product volatiles being trapped in the low molecular weight copolymer salt reaction product. Discoloration often results as a result of excessive exposure to heat and the presence of oxygen at elevated temperatures during the preparation of these low molecular weight copolymer acid salts.